1. Field of Invention
This invention relates to devices for electrically counting the number of persons entering and/or exiting a given area and more particularly to electrical devices for electrically counting the number of persons entering or exiting a given area which also ascertains the direction of movement of the person entering or exiting.
2. Prior Art
In the prior art there are several methods which have been used to count the number of persons entering or exiting a given area. Such methods include: (1) methods in which the counting is done by hand; (2) optical methods; (3) methods utilizing ultrasonic waves; and (4) methods using mat swithces. However, all of these methods suffer from some drawback.
With the methods in category (1) the personnel related cost are very excessive and it is impractuial to utilize such a method for a daily count. Also, error is introduced when large numbers of people are entering and/or exiting at the same time. Methods in category (2) which use infrared or a visable light beam count the number of the times that the beam is interrupted. By installing beams in several locations, the method of category (2) can also be used to ascertain the direction of movement of the person entering or exiting the controlled area. However, when the number of persons entering or exiting the area overlaps with each other as is commonly the case, the methods of category (2) count a single person. Furthermore, in the methods of category (3) ultrasonic waves are emitted and the Doppler effect of the reflected waves is used to count the number of persons entering or exiting the area. However, the board emission pattern makes it impractical to use the method of category (3) when persons are entering and/or exiting in a continuous stream of traffic. Furthermore, it is not possible with the method of category (3) to ascertain the direction of movement of the persons entering or exiting. In the methods of category (4), mat swtiches are installed at the entrances and exits of the given area. The number of persons who step on the mat switches is counted. However, the mthod of category (4) suffers from the drawback of counting only one person when a number of persons are present on the mat switch at the same time.